Starting and operating of fluorescent lamps



Oct. 14, 1947.

R. w. KEISER, ETAL' STARTING AND OPERATING OF FLUORESCENT LAMPS FiledJan. 18, 1943 3 Sheets-Sheet- 1 a /7 P a V 4 p5 7 --z a \g T gvwoz/wlkwOct, 14, 1941' R. w. KEISER ET AL I 2,429,162

STARTING AND OPERATING OF FLUORESCENT LAMPS Filed Jan. 18, 1943 sSheets-Sheet 2 1 ,1947. R. w. KEISER EIAL STARTING AND OPERATING OFFLUORESCENT LAMPS 3 Sheecs-Sheet 3 Filed Jan. 18, 1943 Patented Oct. 14,1947 STARTING AND OPERATING OF FLUORESCENT LAMPS Russell William Keise rand Charles Philippe Boucher, Fostoria, Ohio, assignors to Boucher andKeiser Company, Atlanta, Ga., a partner ship Application January 18,1943, Serial No. 472,768

I 13 Claims.

This invention relates to fluorescent lamps and more particularly tocircuits and apparatus for starting and operating such lamps from normalsources of power supply.

It is a general object of the present invention to provide novel andimproved apparatus and circuits for cold cathode starting and normaloperating one or more lamps of the fluorescent type from a commercialsource of alternating current.

More particularly it is an object of the invention to provide circuitsand apparatus capable of providing the necessary excess potential forthe cold cathode starting of lamps of the fluorescent type and forsubsequently providing the exact operating potential and current for thenormal lighting of these lamps.

It is an important object of the invention to provide the additionallamp starting potential without using any increased quantity of copperor iron above that necessary to provide the normal operating voltage andcurrent for the lamps under optimum conditions.

It is an important feature of the invention to provide a transformer,adapted to be interposed between a normal source of alternating currentat commercial potential and one or more lamps of the fluorescent typewhereby for regular operation of the lamps a suitable potential andcurrent is provided, together with automatic means to temporarily givean increased turns-ratio between the primary and secondary of thetransformer for supplying a substantially higher potential available tostart the lamps by the cold cathode method.

Another important feature of the invention consists in the switchingarrangement, which, under cold lamp conditions so associates the partsof the circuit, that, upon closing the main power switch a high startingpotential is applied to the lamps and is automatically reduced uponlighting of the lamps to that necessary for their normal operation.

An additional object of at least one embodiment of the inventionconsists in the automatic switching of current limiting resistors intothe lamp circuits during the starting operation to limit the arccurrents to values low enough to ensure against damage to the filamentsof lamps built for hot cathode starting but used in accordance with thepresent invention for cold cathode starting.

A still further object of that particular embodiment includes delayedaction switching which is timed to occur when the filaments of theelectrodes have obtained a proper emissive temperature as a result ofthe action of the striking are,

Figure 1 is. a schematic and diagrammatic showing of a circuit andapparatus for starting,

and operating a pair of fluorescent lamps from a conventional source ofalternating current, making use of a heat actuated switching device foreffecting the voltage changes.

Figure 2 is a View similar to Figure 1 but show ing a relay typemagnetic switching device;

Figure 3 is a view similar to Figure 1 but showing a modified thermaltype of starting switch;

Figure 4 illustrates a circuit in which the reactances normally used forregulating the current flow to the several lamps are combined with thesecondaries of the transformer; V

Figure 5 shows a further embodiment of the invention;

Figure 6 shows a still further embodiment for the operation of aplurality of lamps;

Figure '7. is a diagrammatic arrangement of a core structure which maybe used when magnetic shunts are indicated in the transformer magneticcircuits; and

Figure 8 illustrates a further embodiment of the invention incorporatingdelayed action switching from starting to operating conditions togetherwith automatic current limiting features active only during the startingoperation.

With the increasing use of fluorescent lamps for general lightingpurposes there has been an insistent demand for an improved system forstarting such lamps, since the ones in vogue at the present timeinterpose too much delay between the closing of the power switch and theactual striking of the are which causes the illumination in the, lamp.

Most lamps are now lighted by making use of starting systems involvingthe filaments in the two ends of each lamp which are first heatedtoincandescence after which a high potential resulting from a reactancekick'following a circuit change is relied on to establish the arc.Certain automatic starting switches are provided which first connect thetwo filaments in series into the power source until they becomeadequately heated, After a certain time delay the starting ments of apotential much higher :than the 'normal operating potential, and as soon:as .the arc is struck, this voltage is reduced to just the requisiteamount to maintainzthat.characteristic of are which will providetheidesiredjlight emission from the lamp as well as the'length of lifecommensurate with that provided by the use of the previously describedtype-of starting-operation.

It has heretofore been proposed to start fluorescent type lamps by theuseof high potentials withcoldcathodes, but these systems have eitherfailedtoproperly reduce the voltagefor normal operation, whereby thelife .of the lamp was shortened, .o'r .h'avenecessitated the use of toogreat. .quantitiesof copper-and 'ironin the startingand operatingapparatus. .In accordance with thepresent inventiona minimum use is madeof these critical .inater 'ls and ;no additional .material, above thatrequired for normal operation, is=inc1udedin the apparatus .in-spite ofits ability to provides .high .striking .voltage for starting purposes.l

eierringfirst to Figure 1 ior oneembo'diment -.of the invention, there.is illustrated a pair of conventional fluorescent lamp .tubesJfl and H.each havingend laments l4 (each of which is connectedtoa -p1ai-r.ofvpinilliiat .one end of the .tube. These pins are connected together, as

shown in accordance .withthepresent jinvention,

sothat thefilaments. are individually, shorted and -actsolelyraselectrodes. ZITolimit the current supplied to thefiu'o'rescent typelamps, which have what is known as fnegative resistance, suitablereactors it and-l] are associated withthelarnps.

Where two similar lamps are simultaneously lighted on one circuit it ispreferred to use a dual form of reactor such as illustrated in the co-;pending application ofBussellWJKeiser, Serial Y9.- filed May 29,1342,for .Reactances, which issued October 30, .1945asi1lnited States PatentNo. 2,387,797, in which the ,two windings :such-as J5 and ll are mountedon a single core provided with appropriate air gaps to produce highleakage reactance. .Obviouslythelamps are eonnected in Parallel so that.either one alone could be independently operated if desired withoutunbalancing the system,

O.neend ofone of the windings i6 is directly connected byeonductor [8 toone end of the tube [0, .while the other winding 11 has one end con- ..nctediby conductor .[9 ,toone end .of tube H. A Qditable condenser .29 isinterposed in the con- ..duc'to'r 19 to improve the power factor .of thewhole circuit and obviate strobsoscopic efiects :from the lamps as is.welleknown.

The ivcommon terminal 2] of the two reactors 'i's connecte'd by wire 2,2to one end 23 of the condarypfa special transformer and the oppositefend 2.4 of this secondary is connected by wire .25 to the rem iningterminals at the oppoaite ends .of both lamps.

y; ,In this embodiment the transformer is of the autoeconnected type,the full number of turns of Ithewinding between .;termin als 23 and 24representing the secondary and a section. thereot bebecause tweenterminals 24 and 26 representing the normal or operating primary. Asource of alternating current, at a suitable commercial potential, isshown at 28 connected through a switch 29 and wire 30 to the terminal26. In normal operation the terminal "24' is also connected to thesource of power 28 through wire 3|, contact 32 of switch 33, movablecontact 34 of this switch, and coniluctor 35. Under these conditions theturnsratio between the primary 24, 26, and the sec- :ondary .23, 25, issuch as to provide the exact optimum operating potential from the source28 to the :lamps, Ill. and ,1 I, the current being held to thepredetermined proper amount by the design of the reactors I6 and I1.

For starting fluorescent lamps by the cold cathb'de'method a voltage atleast 50% higher than that necessary or desirable for normal operationis required and in this embodiment of the invention it is provided bychanging the turnsratio bet-ween the effective portion of the primaryandthe secondary. Thismea'ns a reduction in the number ofturns on-theactive section of the primary and for this-purpose atap is made at 3!and connectedby wire 38 to contact 39 of switch 33. Under the proper"positioning of the contacts in'the swith, as shown in the drawing, thisconnects the source 2-8 to the section 26, 31 of the primary, havingles's'turns than the whole or'norm'al operating portion of the primaryand of the now higherturns-ratio between secondary and primary anadditional voltage is supplied to the lamps for striking the arcs andstarting them. V

The switch illustrated at 33 is only one of a number of types suitablefor changing from starting-to operating conditions. The switch shown ispreferably enclosed in an evacuated bulb to reduce sparking or arcingand to thermally insulate a iii-metallic elemer'i't therein from thesurrounding atmosphere. )The switch comprises three contacts 32, 34,and3 9 each carried on the end --of .a'long'arm. The supporting arm tofor {the}: "ntact 134 is 'abi metallic element, and is initially"adjusted 'to close, the circuit between contacted andcontact 39 whenthe element '40 "is' lcold. This conditions the circuit for startingtheflamps and'thearcs jump'through the lamps upon'closing the'swit'ch 29becaus the curtailed "section of the primary is energized and producesahigh secondary voltage. During this starting operation current flow tothe primary is held to desired safe limits by-the resistor 42 interposedin conductor 38.

{The current flowing to the primary through "the bi-metallic'element'45, resulting from th operation of the two starting arcs is sufiicient"to heat the arm "40 and cause the contact 34 to moveover and engagecontact 32. Since this is a relatively slow operation, it is desired tohave contact 39 remain in engagement with contact '34 until the circuit32, 34 is closed, thereby preventing extinguishing of the arc.

This is readily efiecte'dby having the supporting arm for contact '39'otspring material and operating circuit and the arc will not beextinguished. The resistor 42 previously mentioned prevents a completeshort circuit of that section of the primary between 24 and 3! while allcontacts 32, 34, 39 are in engagement.

The starting operation is of extremely short duration so that themomentary overloading of both the primary and the secondary as well asthe core of the transformer has no detrimental eifect so that thistransformer can be designed to have only th requisite amount of bothcopper and iron to take care of its normal operating load. By using thissystem starting is achieved in an improved manner without the necessityof using any additional material in the system over that used for normaloperation since the starting switch 33 need not be substantially largerthan the usual starter, one of which is supplied with each lamp in thehot cathode starting system.

The circuit of Figure 2 does not difier substantially from that ofFigure 1 and a detailed description of the whole circuit is notessential.

The main difference is in the switch which is of the magnetic typerather than the thermally operated type of Figure 1. It comprises arelay-like device having an operating coil or magnet 60 interposed inthe conductor BI leading from terminal 24 of the secondary of thetransformer to the left hand ends of both lamps. The armature 62 of therelay is connected by conductor 63 to the source of power 28 in the samemanner as the bi-metallic arm of switch 33 while the opposite end ofthis source of power is connected to the primary terminal 26 of thetransformer. The back contact 64 of the relay, with which the armatureis in engagement when the magnet is unenergized, is connected throughresistance 42 and wire 65 to the tap 3'! on the primary of thetransformer. The front contact 65 of the relay is connected to the wire6| which leads from the coil 60 directly to the terminal 24 of thesecondary of the transformer.

In operation, with the parts in the position shown, a closing of themain switch energizes the section of the primary between the terminals26 and 37 and produces a high secondary voltage which flows to the lampsstriking arcs therein. When these arcs strike, current flows in thewinding 60 from the secondary of the transformer, energizes the magnetand transfers the armature from the back contact 64 to the front contact66 so that current from the source 20 is transferred from the tap 37 onthe primary to the terminal 24 thereof. There is always a holdingcurrent which flows in the magnet 60 to maintain it in operatingcondition as long as the lamps are lighted. The contacts of the relaymay either be arranged, in any Well-known manner, to close at 66 beforebreaking at I54 or recourse may be had to the speed'of operation toeliminate the necessity for this. In the event that it is desired topermit the starting arcs to flow in the lamps for a short interval, toheat up the tubes to insure operation at the lower normal temperature,the relay may be made of the slow acting type, by any of the well-knownexpedients, such a the placing of a large copper slug 68 on the corethereof.

In Figure 3 is shown a system for obtaining a change in turns-ratiobetween the primary and secondary windings wherein the source of power28 is arranged to be connected always to the whole primary windingbetween terminal I00 and IOI. An auto transformer is again shown.

The secondary of this transformer is represented by the whole windingbetween IOI and H32. The secondary is tapped at I03 to produce a sectionIOI, I03 for supplying the normal operating potential to the lamps. Thisis indicated .as having fewer turns than the primary for use with lampsrequiring less operating potential than that provided from the source.

The two lamps and their reactors are connected exactly as in Figure 1and it remains only to describe how either the whole secondary or aportion of the same is used for energizing them. The lead I04 from thecenter of the reactors is connected to the bi-metallic element I05, ofan evacuated switch I06, which carries the contact I01 normally inengagement with contact I08 connected by wire I 09 to the end of thesecondary at I02 through the interposed resistor III Under theseconditions a high secondary to primary turns-ratio exists and a strikingpotential is provided between points l0l and I02 of the transformer forstarting the lamps. Within the envelope I06 is glow terminal II2connected to an intermediate position H3 on the secondary of thetransformer. This electrode, being at a different potential than any ofthe other electrodes in the switch envelope, which may be suitablyfilled with a quantity of ionizable gas and provided with an emissivematerial causes a glow discharge to be set up, the heat from whichcauses the bi-metallic supporting arm I05 of contact I01 to move towardthe right and eventually engage contact II5 subsequent to which it dis'engages contact I08 in the same manner as described in connection withFigure 1. When this operation is completed only that portion of thesecondary between IOI and I03 is applied to the lamps for operatingthem. There still remains within the switch a difference of potentialbetween the glow electrode and the others which maintains the glow tohold the bi-metallic element stressed toward the right during all of theoperation of the lamps. When the main circuit is opened to extinguishthe lamps the glow is extinguished and the contact I01 returned to theposition illustrated in the drawing ready for a restarting of the lamps.

In Figure 4 is illustrated a circuit in which a transformer having aprimary separate from the secondary is used. This circuit also leads tothe elimination of the reactors for the lamps, their function beingperformed by the separate secondaries one for each lamp in a mannerwhich will be later described. Referring now to this drawing it will beseen that the separate primary winding comprises a number of turnsbetween terminals 200 and MI, there being an intermediate tap at 202.The source of power 20 is arranged to be connected by suitable switchingcontacts 204 to either the whole primary or that portion of the samebetween 200 and 202. When in the second position the resistor 205 isinterposed in the circuit.

Two identical secondaries, where identical lamps are used, arerepresented at 20? and 2 08, the first being connected through acondenser 209 to lamp 2I0 and the second being directly connected tolamp 2| I. The two lamps are connected together at 2I2 and through thesmall winding 2I3 back to the connected ends of the secondaries. Thewinding 2I3 represents diagrammatically the magnet for operating thecontacts 204 in the same manner as the magnet 60 in Figure 2. I

It will be seen that when the arrangement'of of the three lamps.

'contacts is such that the source of power is con- :nected between 200and 202 a high secondary to primary turns-ratio exists and strikingvoltages are provided in each secondary, wherea when the whole primaryis energized a lower or operating voltage is provided for-each of thelamps.

In order to prevent excessive current flow to each of the negativeresistance lamps, suitable magnetic shunts are arranged in the commoncore ofthe transformer to provide a high leakage flux which producesa-counter-E. M. F. in the primary winding and hence reduces the currentflow and the output of the transformer. This leakage reactance may beachieved through the use of a core section somewhat as illustrated inFigure '7.

Here the core includes three connected legs 215, 216, and 211, thecenter one of which is provided with the primary winding and the outerones with the secondary windings respectively. The connecting portionsof the core structure at the top and bottomare designated-2 I 8 and 2 I8respectively, The magnetic shunts are shown at 220 and 22! and may beprovided with air gaps as at 222 if desired. These same shunts arediagrammatically represented in Figure 4 at 220 and 221 as existingbetween the sections of the coils on the common core.

The resistor 205 shown in Figure 4 serves the same purpose astheresistor -42 in Figure 3, that of limiting the current when only aportion of the primary is in operation. The circuit of Figure 4 uses aminimum of critical materials since no separate reactors are requiredand no additional metal is needed in the transformer above the absoluteminimum used for normal operating.

The circuit of Figure 5 is not substantially different from that ofFigure 2 except that the primary 300, which is tapped to change theturnsratio in the manner described in connection with Figure 4, isentirely separate from the secondary 301 instead of being arranged as anauto transformer as shown in Figure 2. The operating coil 303 for therelay is shown connected between one end of the secondary and theintermediate tap on the reactors 304.

The circuit of Figure 6 is similar to that of Figure 5 buthere thesinglesecondary 400 is connected to oneend of each of three reactors40!, 402, and 403. These may be on a common core, as shown andconstructed in accordance with the previously mentioned application orthey may each be independent. The-opposite end of the secondaryis,-through wire 404, connected to one end of each of the three lamps405, 406, 401. The .opposite ends of each of the reactors are connectedto the remaining ends respectively of the several lamps. The circuit ofat least one of the lamps is provided with the power-factor changingcondenser 408. The relay operating coil M0 is so interposed in thesecondary circuit that current to all three lamps must flow through it.In this manner, by properly designing this coil, the circuit may bearranged so that there is no transfer of the'source of potential fromthe partial to .the whole primary until an arc has struck in each Thisprevents premature operation which might leave one or two lampsunilluminated. It will be noted that this characteristicalso applies tothe arrangements of some of the other figures and is largely controlledby the use ofso-called marginal relays which do not close unless thecurrent flow through them exceeds a predetermined minimum.

Fluorescent lamps which are especially de- --signedfor cold cathodestarting do not have filament electrodes intended to be heated forstarting, an'dit 'hasbeen found particularly desirable, especially foroutdoor operation, to use high current densities for their startingsince this vaporizes the mercury more readily and heats up the .gaswithin the tube quickly. Such lamps, however, are not readily availableon the market and recourse is usually had to the so-called filamentelectrode type of lamp intended for hot cathode starting by heating thetwo filaments to incandescence. These filaments are coated with anelectron emissive material and are readily damaged by excess operatingtemperatures so that care must be exercised, in starting by the coldcathode method, to limit the current densities to those which are safeand will provide normal or extra life for the filaments. Unfortunatelythe current limiting devices, such as reactors or the like, used to holddown the normal operating current to a safe value are of insufiicientimpedance to limit the starting current at the much higher startingvoltages.

In the embodiment of the invention illustrated in Figure 8 a circuitarrangement is shown which provides additional impedanceto thecurrent-only during the starting operation and switching mechanism isarranged not only for inserting and removing this impedance but formaking the change-over from the starting to the operating voltage andvice versa in a manner somewhat similar to those already described.

Referring now to the figure, it will be seen that it makes use of anautotransformer 500 although obviously separate windings might be usedin the manner illustrated in Figures 4 and 5. This transformer containsa two-section primary, that bearing the reference character 50! beingused for starting purposes, and this portion plus the section 502 being.used for operating purposes whereby, under the latter-condition, theratio of turns to that of the secondary winding 503 is lower.

A source of alternatingcurrent 580 and a main switch 505 are connectedto the end 5136 of the winding on the transformerand, through an aumaticswitch including contacts 581 and 598 which are always closed when theswitch 585 is open, this source ofcurrent is also connected to theterminal 501 of the starting section of the primary. The terminal 566 ofthe transformer is connected by conductor 509 to the left-hand ends ofthe lamps'5I 0 and M2, the current passing by way of conductors 514through a relay coil 5L5. The secondary terminal M8 is connected by awire5i9 to the junction 5280f a pair of starting resistances 52L whoseopposite ends are respectively connected to the two ends of the balancedreactor coils 522 and 524, exactly like those shown in Figure 1. Theremaining terminals of the reactor coils 52-2 and .524 are connected tothe opposite ends ofthelamps bid-and 512, a condenser'525 beinginterposed in enact the circuits to improve the power factor-andeliminate .stroboscopic effects.

Under the conditions illustrated and just described, the closing ofswitch 505 energizes primary section 50l of the transformer anda highpotential is induced between the terminals 555 and 513 of thetransformer which is applied to the opposite ends of the lamps throughthe current limitingreactors -52'2 and 524 each inseries with one of theresistors 52!. The reactors 522 and 524 aredesigned to-hold down theoperating 9 the starting current to the desired low figure when thevoltage is much higher. They are therefore augmented by the'simpleresistors 52! in series therewith for this purpose. For operating thelamps, however, it is desired to increase the number of turns in theprimary so that its ratio to the secondary shall be lower, whereby theoverall induced voltage applied to the lamps will be sufiiciently lowfor continuous operating purposes, when the reactors alone are adequateto limit the current. The switching operation to transfer from startingto operating conditions must therefore include means to remove theresistors 52! from the'lamp circuits.

A composite relay shown in the dotted line box 530 takes care of all theswitching. It is actuated by the coil !5 which is adequately energizedonly when the arcs strike in the two lamps, since it is inserted in themain conductor 509 leading thereto. When this coil is energized, itpulls down its core attached to the insulating frame 53! which closesthe spring mounted contacts 532 and 533, the former being connected bywire 534 to terminal 535 at the end of the operating primary comprisingthe sections 50! and 502. Lower contact 533 is mounted on the samespring as the lower contact 508 on the switch which closes the startingsection of the primary. When the spring carrying contact 532 movesdownwardly, a circuit is closed at 532, 533, and one is opened at 50'!and 508, thereby applying the source of alternating current across thetwo primary sections 50! and 502 in series, and disconnecting it fromthe single section 50!. This provides proper operating voltage from thewhole winding of the transformer.

A three-contact switch is also operated by the frame 53! on itsdownwardly movement and serves to shunt the two resistors 52! for whichpurpose the middle connection 52!] thereof is connected to the springcarried contact 537, while the opposite ends of the two resistors areconnected respectively to spring mounted contacts .538 and 539. When theframe 53! is drawn down wardly by the relay winding 5l5, the threecontacts 531, 538, and 539 are drawn together, shunting out theresistors and connecting the inner ends of the reactor windings directlyto terminal 5l8 of the secondary. Operation is now exactly asillustrated in connection with Figure 1 or 2.

. For starting a hot cathode type of lamp by the cold cathode method, ithas been observed that the best results are obtained if this is achievedin three steps: first, the striking of an arc of just sufiicientintensity so that it will locate itself at some point on the filament ofthe electrode which is coated with emissive material; second, theregulation of the arc current to just a sufficient intensity to bringthe striking point on the filament to an electron emissive temperaturein a predetermined time; and third, the transfer from starting voltageto operating voltage only after the filaments have attained thisemissive temperature. The circuit just described in connection withFigure 8 permits obtaining these desired results since the intensity ofarc current can be regulated by changing the size of the resistors 52!.The time elapsed between closing the starting circuit and transferringto the operating circuit can be regulated by means of the relay 530which may be of the time delay type. The time delay may be obtained byany well known means, such as the use of a thermal relay, a dash pot, amercury pocket, or the well known use of a heavy metal slug such asshown at 540associated with the core or winding of the relay. It will beappreciated of course that there is no current flow in the relay windinguntil the striking of the arcs in the lamps, although the startingcurrent may have been applied for several seconds. The time delayinterval will therefore occur between the instant of striking of thestarting arcs or are and the time of transfer from the starting to theoperating condition. This period can be regulated, in the initial designof the relay, or can be made variable to take care of different types oflamps. If a cold cathode type of lamp is used, no time delay isnecessary and the transfer can take place immediately upon the strikingof the starting arc.

The above described circuit arrangement is of importance, for thecontacts are so disposed in the circuit that only one pair of them opensunder load. The contacts 50! and 50B are separated while carryingcurrent. The others are only closed under what might be termed loadconditions, but since contacts 532 and 533 practically shunt 50'! and508 while they are being opened, there is not much chance for theselatter contacts to burn. The remaining contacts do not open until themain switch 505 has been opened and all current has stopped flowing.They can therefore be relatively small, not only because they do notopen under load but because they carry relatively low currents and foronly brief intervals during the starting operation. A simple and compactrelay of the telephone type can therefore be used which is good formillions of cycles of operation. I

As an example of the values of voltage, current, resistance, and thelike, the following may be noted as an optimum arrangement forcontrolling two 40-watt fluorescent lamps as arranged in the circuit ofFigure 8:

Operating alternating current sourcevolts Operating voltage across thelamps200 Striking voltage across the lamps400 Resistance of resistors52!1200 ohms each Capacity of resistors 52!-20 watts each Strikingcurrent-.2 ampere for each lamp Operating current-.4 ampere for eachlamp Current in relay coil 5!5.4 ampere Resistance of coil 5l5-8 ohmsOperating loss in relay3.2 watts Time delay in relay- 2.5 seconds Thearrangements of circuits and apparatus as shown are suitable for theoperation of any desired negative loads and cannot be the cause of anyuncontrollable potential or current disturbances. Under ordinarycircumstances starting voltages are needed only for short periods, sayfor considerably less than one second to a maximum of 30 seconds. Suchvoltages are not dangerous in equipment designed for normal operation atlower voltages because of the short time interval precluding any undueheating in the copper or iron.

Having thus described the invention, what is claimed as new and desiredto be secured by Let- .ters Patent is:

v 1. In a circuit for starting and operating fluorescent lamps, thecombination with a source of alternating current and a lamp adapted forcold cathode starting, of a transformer having a primary winding and asecondary winding, circuit means connecting'the secondary winding withthe lamp, circuit means connecting the primary winding with the sourceof potential and means under control of the current delivered to the 11lamp to change the turns-ratio, or primary to secondary to provide firsta'high starting voltage for striking an arc in the lamp and then a loweroperating voltage.

2. In a circuit for starting and operating fluorescent lamps, thecombination with a source. of alternating current and a lamp adapted forcold cathode starting, of a transformer having a secondary winding,circuit means connecting the secondary winding with said, lamp to supplycurrent for the same, aprimary winding having the correct turns-ratioandcurrent carrying capacity for optimum operationof the secondary fornormal burning of the lamp, means'temporarily to connect said source to.less than the full number oi turns of the primary to in'duoea highstartin voltage in the secondary and means automatically to connect thewhole primary to said source to induce the desired operating voltage insaid secondary upon the flow of starting current in the lamp.

3. In a circuitfor. starting and operating fluorescent lamps, thecombination with a source of alternating ourrentand a lamp adapted forcold cathode startingof a transformer havin a primary winding and asecondary winding, circuit means connecting the primarywinding directlywith the said source, circuit means connecting the full secondarywinding with the lamp when the primary is die-energized andautomatically time lag switching means to transfer the lamp to a portionof the secondary sufficient to provide proper operating voltagetherefor, said time lag means being responsive to voltage in the.transformerwindings,

4. In a circuit for cold cathode starting and normal operation ofaplurality of fluorescent lamps, the combination with a source oralternating current at a commercial potential, and a plurality of lamps,of, a transformer having a secondary windingf'or and; connected to eachlamp and a, single primary winding, the primary winding having asuitable turns-ratio to each secondary to supply the-connected lamp withthe proper operating potential, said primary having a tap connected witha, lesser number of turns having such a ratio tcthe secondaries as. tosup.- ply high starting potential to the associated lamps, a relaybiased to connect the tapped portion of the primary with the source ofcurrent and a magnet coil connected to be energized by current flow toone of, said lamps to operate the relay to connect the source to thewhole of said primary.

5, In a circuit for cold cathode starting and normal operation of aplurality of fluorescent lamps, the combination with a source ofalterhating current at a commercial potential, and a plurality of lamps,of a transformer having a secondary winding for and connected to eachlamp anda single primary winding, the primary winding having. a suitableturnseratio to each secondary to supply the connected lamp with theproper operating potential, said primaryhaving a, tap connected with alessernumber of turns havin such a ratio to the secondaries as to supplyhigh starting. potential to theassociated lamps, a relay biased toconnecttheitapped portion of the primaryv with, the'source of currentand a. magnet coil nn cted. to'bei nersi d b ur nt flow tqall of,sai dlampsto operate the relay to connect thesour'ce to the whole of saidprimary, said coil having such characteristics that it does not overcomethe bias until starting current is flowing tolall ofthe lamps.

6. In a circuit for cold cathode starting and q 'r t n f a luor centlama he om;- I

bination with a, sourceof. alternating current at a. commercialpotential and a lamp, of a trans,- former having a secondary winding,connected to the lamp and a primary of suitable turns-ratio to providethe correct operating voltage for the lamp, a core for said transformer,an intermediate tap on said primary, aswitch to alternatively apply thesource to thetapped portion of or the whole primary forv respectivelystarting and operating the lamp, the primary winding wire size and thecore volumebeit g lust'large enough to handle the normal operating loadand hence temporarily overloaded when the tapped portion of the primaryis connectedtg the source.

'7. In a circuit for cold cathode starting and normal operation of afluorescent lamp, the combination with a source of alternating currentat a commercial potential and a lamp, of a trans former having asecondary winding connected to the lamp and a primary of suitableturns-ratio to provide the correct operating voltage for the lamp, anintermediate tap on said primary, 2. switch biased to connect the tappedportion of the primary to said source and movable to connect the wholeof the primary to said source, said switch being arranged to completethe second mentioned connection before the first is broken, and means inthe primary circuit to limit the current flow therein during the circuitchanging operations of the switch.

8. In a circuit for cold cathode starting and normal operation of afluorescent lamp, the combination with a source of alternating currentat a commercial potential and a lamp, of a transformer having asecondary winding connected to the lamp and a primary of suitableturns-ratio to provide the correct operating voltage for the lamp, anintermediate tap on said primary, a switch biased to connect the tappedportion of the primary to said source and movable to connect the wholeof the primary to said source, said switch being arranged to completethe second mentioned connection before the first is broken, and means inthe primary circuit to limit short circuit current in any portionthereof during the circuit changing operations of the switch, said lastmentioned means being so connected as to limit the current flow to theprimary during only the biased positioning of the switch.

9. In a circuit for cold cathode starting and normal operation of afluorescent lamp, the combination with a source of alternating currentat a commercial potential and a lamp, of a transformer having asecondary winding connected to the lamp and aprimary of suitableturns-ratio to provide the correct operating voltage for the lamp, anintermediate tap on said primary, a switch biased to connect the tappedportion of the primary to said source and movable to connect thewhole ofthe primary to saidsource, said switch being arranged to complete thesecond mentioned connection before the first is broken, and means havinga time delay action for controlling the movement of said switch frombiased to whole primary position.

10. In a circuit for starting and operating flu- .orescent lamps, thecombinationwith a source of alternating current and a lamp adapted forcold cathode starting, of a transformer having a pri mary winding and asecondary winding,'circuit means connecting the secondary winding withthe lamp, circuit means connecting the primary winding withthe source ofpotential; means to change the turns-ratio of primary to secondary toprovide either high starting voltage or low operating voltage, animpedance normally inserted between the lamp and secondary to limit thestarting current, and means automatically to eliminate said impedancewhen operating voltage is applied to said lamp.

11. In a circuit for cold cathode starting and normal operation of afluorescent lamp, the combination with a source of alternatin current ata commercial potential and a lamp, of a transformer having a secondarywinding connected to the lamp and a primary of suitable turns-ratio toprovide the correct operating voltage for the lamp, a core for saidtransformer, an intermediate tap on said primary, a switch toalternatively apply the source to the tapped portion of or the wholeprimary for respectively starting and operating the lamp, a reactor inthe circuit between the lamp and secondary to limit the operatingcurrent to a predetermined value but being of insuflicient reactance'tolimit the starting current to the desired amount when the higherstarting voltage is applied resulting from applying the current sourceto the primary tap, a resistor connected to augment said reactor duringstarting, and means on said switch to remove the resistance from thecircuit when the source of current is applied to the whole primarywinding.

12. In a circuit for starting and operating fluorescent lamps, thecombination with a source of alternating current, a main switch, and alamp of the filamentary cathode type, having shunting means on thefilaments, of a transformer having a secondary winding, a reactor, saidlamp, secondary and reactor being connected in series for normal lampoperation to provide the requisite operating current and voltage, aprimary winding on said transformer having the correct turns-ratio forexcitation of the secondary for normal lamp operation, switching meansto connect said source to less than the full number of turns of theprimary to temporarily induce a high starting voltage in the secondarywhen the main switch is closed, a supplementary impedance, saidswitching means bein arranged to connect said impedance in the secondarycircuit to limit the lamp current to that necessary for starting at theincreased voltage, and a relay coil for actuating said switching means,said coil being responsive to starting and operating current to changeand maintain the switching means from star-tingto operating condition.

13. In a circuit for starting and operating fluorescent lamps, thecombination with a source of alternating lamps, a main switch, and alamp of the filamentary cathode type, having shunting means on thefilaments, of a transformer having a secondary winding, a reactor, saidlamp, secondary and reactor being connected in series for normal lampoperation to provide the requisite operating current and voltage, aprimary winding on said transformer having the correct turnsratio forexcitation of the secondary for normal lamp operation, switching meansto connect said source to less than the full number of turns of theprimary to temporarily induce a high starting voltage in the secondaryWhen the main switch is closed, a supplementary impedance, saidswitching means being arranged to connect said impedance in thesecondary circuit to limit the lamp current to that necessary forstarting at the increased voltage, a relay coil for actuating saidswitching means, said coil bein responsive to starting and operatingcurrent to change and maintain the switching means from starting tooperating condition, and means to delay the operation of said switchingmeans for a predetermined period after the beginning of starting currentflow.

RUSSELL WILLIAM KEISER. CHARLES PHILIPPE BOUCHER.

REFERENCES CITED The following references are of record in the

